Optical fibers used in communications applications, such as in local area networks, telephone service, cable television service, and the like, involving the transmission of data, including digitally encoded voice and video communications data typically comprise a glass fiber that is provided with at least two protective coatings, including an inner or primary coating applied directly to the glass fiber and a secondary or outer coating applied over the primary coating.
The primary coating serves as a buffer to cushion and protect the glass fiber when the fiber is bent, cabled, or spooled. Stresses placed upon the optical fiber during handling may induce microbending of the fibers and cause attenuation of the light which is intended to be transmitted, resulting in inefficient signal transmission. The secondary coating is applied over the primary coating and functions as a tough, protective outer layer that prevents damage to the glass fiber during processing and use.
Between the two coatings, the inner, or primary coating has the strictest requirements for physical and chemical properties. These requirements include very low modulus, low glass transition temperature, and good adhesion to the glass. Because of these strict requirements, formulations used for preparing the inner or primary coating tend to be somewhat limited in terms of materials used, and also tend to be relatively expensive. In addition, a frequent problem with low modulus primary coatings is that they are prone to defects introduced by fiber processing and/or use in the field. These defects appear as rips in the coatings or delaminations from the glass, resulting in comprised fiber performance, e.g., significant undesirable attenuation.